Detailed explanation of the use of PHP variable functions

PHP supports the concept of mutable functions. This means that if a variable name has parentheses after it, PHP will look for a function with the same name as the value of the variable and try to execute it. Variable functions can be used to achieve a number of purposes including callback functions, function tables.
Variable functions cannot be used in language constructs such as echo(), print(), unset(), isset(), empty(), include(), require(), and similar statements. You need to use your own wrapper functions to use these structures as variable functions.
Example of Example #1 variable function

<?php
function  foo () {
    echo  "In foo()<br />/n" ;
}
function  bar ( $arg  =  '' ) {
    echo  "In bar(); argument was ' $arg '.<br />/n" ;
}
//  use  echo  Wrapper function of 
function  echoit ( $string )
{
    echo  $string ;
}
$func  =  'foo' ;
$func ();         // This calls foo()
$func  =  'bar' ;
$func ( 'test' );   // This calls bar()
$func  =  'echoit' ;
$func ( 'test' );   // This calls echoit()
?> 
 You can also take advantage of the nature of mutable functions 1 Method of an object.  

Example #2 Variable method example

<?php
class  Foo
{
    function  Variable ()
    {
         $name  =  'Bar' ;
         $this -> $name ();  // This calls the Bar() method
     }
    function  Bar ()
    {
        echo  "This is Bar" ;
    }
}
$foo  = new  Foo ();
$funcname  =  "Variable" ;
$foo -> $funcname ();    // This calls $foo->Variable()
?>